This invention relates to a method of forming recloseable packages, profile strips used in the method and packages produced thereby. More particularly, the invention relates to recloseable packages which are made from two film layers hermetically sealed at the periphery of the package and sealed to profile strips having recloseable means elements formed thereon.
A common method of packaging foods such as sliced luncheon meats and the like is by use of horizontal form, fill and seal procedures. In that procedure, a bottom film is placed horizontally over a piece of equipment having a cavity the general size and shape of the article to be packaged. Heat is applied and a vacuum is drawn in the cavity, forcing the bottom film into the cavity. The food article is placed inside the film-lined cavity, and a top film is placed over the article. Heat seals are made between the top and bottom films, often while the resulting package is being evacuated to produce vacuum packed food products.
There has been a recent interest in providing food packages of the type thus produced with recloseable seals. In this regard, see U.S. Pat. No. 4,782,951, which is incorporated herein by reference. Recloseable food packages are generally made from separate films and extruded profile strips, though some suggestion of films with integral recloseable means may be found in the art. In the more common practice, the separate profile strips each comprises a flange and an integral interlocking member. The profile strips are formed by two separate extrusions or through two separate openings of a common extrusion die. One profile strip may have a rib or male member and the other a mating groove or female member. The male or female member extends from the front face of the flange member. The rib and groove form a pressure fastenable and releasable closure mechanism. The back side, or sometimes an extended portion of the front face of the flange, is sealed to the package film so that the closure mechanism is disposed between the package walls adjacent the openable side of the package.
Though there has been some suggestion for applying the profile to the film as soon as the profile is extruded, the more common practice is to wait to apply the profile strips to the film at the time the film is made into packages. In that case, the profile strips are extruded, mated, and rolled up for storage. When used on a horizontal form, fill and seal machine, the profile strips are unwound from storage rolls and sealed to the films used to make the packages.
There have been two procedures for applying the profile strips to the films. In the less common procedure, the profile strips are unwound from storage spools and unmated. Each strip is then independently sealed to the packaging film. One procedure of doing this is to blow hot air on the back of the profile to heat it to its softening point. It then has to be immediately pressed into contact with the film. The primary difficulty encountered with this procedure is getting the combined film/profile strips in proper alignment after the cavity is formed in the bottom film, a product is placed therein and it is time to join the two films.
Due to the difficulty in remating the interlocking members once the profile strips are attached to the film, another more complicated process used is to seal the mated profile strips to the film one flange at a time. In this regard, the equipment manufacturers have developed form, fill and seal machines in which a plow element is used to separate the flange segments of the mated profile strips without disengaging the rib and groove. A heat seal is then made between the bottom film and the back side of the flange of the bottom profile strip. After the food product is inserted into the film-lined cavity and the top film put in place, a plow arrangement is again used to separate the flanges so that the flange of the top profile strip can be sealed to the top film. Heat seals are also made around the rest of the package edges. The primary problem with this procedure is that the equipment is more complicated, a sealing step has to be performed in at least two different places in the process. However, machine manufacturers Klockner-Hooper of Itasca, Ill. and T. W. Kutter of Avon, Mass., have produced machines with the plow arrangement.